This study was conducted to explore whether the non-synonymous single-nucleotide polymorphisms in SCN9A gene can predict individual basal pain perception and postoperative pain intensity in the general population undergoing upper abdominal surgery. Methods: Patients receiving elective upper abdominal surgery under general anesthesia were recruited into this study. Genotyping of SCN9A was carried out by direct sequencing. The investigators measured their preoperative pressure pain threshold (PPT) and pressure pain tolerance (PTO). The visual analog scale (VAS) was used for pain evaluation at rest during patient-controlled analgesia (PCA) treatment 0 h, 12 h ,24 h and 48h after operation. And the PCA press frequency and drug consumption were recorded.

The visual analog scale (VAS) is used for pain evaluation at rest during patient-controlled analgesia (PCA) treatment 48h after operation. And the visual analog scale is from 0 to 10 which 0 represent no pain while 10 represent unbearable pain

The probe of pressure algometer was positioned perpendicularly to the skin surface of the patient, and the investigator applied continuous pressure at approximately the same rate according to the visual LCD display on the algometer. subjects were asked to say "pain" when they started to feel pain during the stimulation. The value from the LCD was recorded as the pressure pain threshold.

The probe of pressure algometer was positioned perpendicularly to the skin surface of the patient, and the investigator applied continuous pressure at approximately the same rate according to the visual LCD display on the algometer. subjects were asked to say "ok" when they started to feel the pain became intolerable during the stimulation. The value from the LCD was recorded as the pressure pain tolerance.

Biospecimen Retention: Samples With DNA

Heparin anti-coagulated blood (2 ml) was collected from the central venous during the operation and all blood samples were stored at -80℃. Genomic DNA was extracted from the blood samples using a guanidinium isothiocyanate method.

Patients with the following diseases were excluded: known history of chronic pain, psychiatric diseases or communication disorders, diabetes mellitus, severe cardiovascular diseases, kidney or liver diseases with poor hepatic function, alcohol or drug abuse, heavy smoker, pregnancy or at the lactation period.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01507493